1. Field of the Invention
The present invention relates to a photovoltaic device, and more particularly to a photovoltaic device comprising a semiconductor junction of a crystalline semiconductor such as a single crystalline semiconductor or a polycrystalline semiconductor and an amorphous semiconductor.
2. Related Art
In recent years, there has vigorously been developed a photovoltaic device using a thin film semiconductor. The area of a photovoltaic device using a thin film semiconductor as a power generating layer can easily be increased and the basic requirements for the photovoltaic device such as a solar cell can be satisfied sufficiently.
However, since the thin film semiconductor has a disordered crystalline structure, it has a large number of unbonded sites or ends on a crystalline structure and is not a good material as compared with the crystalline semiconductor. For this reason, there is a problem in that a high photoelectric conversion efficiency cannot be obtained.
In order to solve such a problem, there has been proposed a photovoltaic device in which a crystalline semiconductor substrate and an amorphous semiconductor film having conductive types reverse to each other are bonded. In such a photovoltaic device, since the crystalline semiconductor substrate is used as a power generating layer, a high photoelectric conversion efficiency can be obtained.
Moreover, there has been proposed a photovoltaic device having such a structure that a thin intrinsic amorphous semiconductor film is inserted between a crystalline semiconductor substrate and an amorphous semiconductor film so as not to substantially contribute to power generation in order to reduce the recombination of photo-generated carriers in an interface state generated by a semiconductor junction.
In recent years, however, the application of solar cells has begun to expand to use for personal houses, and an expectation for solar cells to provide clean energy has been increased. Furthermore, it has been required that the conversion efficiency of the photovoltaic device can be further enhanced.